In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station (e.g., BTS, RBS or NodeB). A cell is a geographical area where radio coverage is provided by the radio equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The radio base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a control node known as a base station controller (BSC) or radio network controller (RNC). The control node supervises and coordinates various activities of the plural radio base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which, at least in some respects, builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to user equipment units (UEs).
In many radio access networks the radio base station is a concentrated node with essentially most of the components being located at concentrated site. However, a radio base station can also be configured with a more distributed architecture. For example, a distributed radio base station can take the form of one or more radio equipment (RE) portions that are linked to a radio equipment control (REC) portion over a radio base station internal interface.
One example of an internal interface of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station is the Common Public Radio Interface (CPRI). The Common Public Radio Interface (CPRI) is described in Common Public Radio Interface (CPRI) Interface Specification Version 3.0 (Oct. 20, 2006), which is incorporated by reference herein in its entirety.
Other documents describing developments relevant to Common Public Radio Interface (CPRI) include but are not limited to the following (all of which are incorporated herein by reference): U.S. Patent Publication US-2005-0105534-A1 entitled “Encapsulation of Diverse Protocols Over Internal Interface of Distributed Radio Base Station”; U.S. Patent Publication US-2005-0105552-A1 entitled “Encapsulation of Independent Transmissions Over Internal Interface of Distributed Radio Base Station”; and (3) U.S. Patent Publication US-2005-0107124-A1 entitled “Pre-Start-Up Procedure For Internal Interface of Distributed Radio Base Station”.
In a distributed radio base station node comprising radio equipment control (REC) portion and a radio equipment (RE) portion, information transfer between the radio equipment control (REC) portion and the radio equipment (RE) portion occurs by use of a parallel control word transmitted over the radio base station internal interface (e.g., over the CPRI interface). Data communication by the radio equipment control (REC) with a network side of the radio base station and beyond, as well as data communication by the radio equipment (RE) portion with the transceiver side of the radio base station and beyond, occurs by serial communication. Thus, serial links are connected to both the radio equipment control (REC) portion and the radio equipment (RE) portion of the distributed radio base station. There has been imposed a requirement to use asynchronous serial communication, such as RS485 or RS232, over these serial links, and thus for information exchange between the radio equipment control (REC) portion and the radio equipment (RE) portion.
What is need therefore, are method, apparatus, and techniques for facilitating use of variable baud rates by a distributed radio base station.